The Effect Of Solvent Pretreatment On Coal Pyrolysis And Coal Structure

In order to improve the quality of coal tar, low temperature pyrolysis was carried out in a fixed bed pyrolysis reactor. The effect of pretreatment of solvent and metamorphic grade on the coal pyrolysis behavior was studied. The structure and free radical concentration in coal were monitored by the solid 13C-NMR and EPR to study the mechanism of solvent pretreatment on coal pyrolysis. The results show that the precipitation yield is more from low rank coal. The precipitation yield increases with the increasing pyrolysis temperature and the optimal condition is 600 ℃,15min. The pyrolysis tests were inhibited at CO2 atmosphere because of the lower precipitation yield than that at N2 atmosphere. The activation energy of pyrolysis is also higher at CO2 atmosphere. The weight loss is almost the same with the different heating rate, however the temperature of maximum weight loss rate increases with the heating rate increasing. The contents of oxygen-containing gas increase slowly and the hydrogen-containing gas in pyrolysis gas increases sharply with the increasing temperature, especially at 600 ℃ (the max gas educt rate is 4ml/min). The free radical concentration in the char increases with the increasing temperature, especially after 500 ℃. The free radical concentration in char has a peak value with the increment of residence time.With the increasing temperature, the Hexane Soluble (HS) yield increases. However, the THF Soluble (THFS) yield decreases by the treatment of tetralin, which verified as a good donor for hydrogen. The aliphatic carbon and oxygen-linked carbon decrease, the aromatic carbon increase after treated with solvent. The coal treated by solvent can weaken the non-covalent bond. The aromatic carbon increases. The free radical concentration in treatment coal increases with the increasing treated temperature by the treatment of methylnaphthalene. The pyrolysis characterized temperature increases and the pyrolysis precipitation yield decreases after treatment. The changes of carbon structure have the same trend with the solvent treatment. The Hexane Soluble (HS) yield increases. However, the THF Soluble (THFS) yield decreases after hydrothermal treatment at CO atmosphere with the increasing temperature. When the initial pressure rises, the HS, THFS and total yield increase after treatment. The THFS is higher and the HS is lower at a lower coal-water ratio.